Maybe i can help a little although I am busy atm. I have done only some items STIs so far. Never tried to edit or create map features.
IIRC i once saw good tool for making isometric graphics on this forum somewhere... I ll try to find it.

I suggest getting your hands on some free Blender 3d models and exporting isometric views without perspective distorsion. It's the easiest way to do it.

The problem is, the models I require are quite special, I need a table saw for example and various other models of woodworking and construction equipment which are usually quite neglected by the 3D Modelling Community except of course you go on some pay-site where you pay $50 for a fricking 3D Model of almost nothing (Most expensive 3D Model I stumbled across was some helicopter model for $500 I think)

Okay I just stumbled across a collection of woodworking equipment which is quite complete, but it would need some adjustment regarding textures and to make every piece of equipment "accessible" by itself Woodworking Machinery

Well probably you can copy the objects to their own scene. I wouldn't worry too much about texturing those, you can "age" them in Gimp/Photoshop later.

Yeah if you're handy with Gimp or Photoshop and if you got the time, for me I am quite occupied with getting the maps done before Christmas and some private matters concerning next year. My GIMP and Photoshop expertise is virtually non-existent. Not to mention, some of the already applied textures are probably totally fine, but a lot of those machines haven't been textured at all, so just aging them wouldn't do the trick.

I mean, it's not that urgent, the stuff won't make it into the next release anyways and I am not asking anyone to do my Job for me, but this is honestly work I have no clue about and no time whatsoever to learn it from scratch. So it would be just great to have someone at the ready, who is able and willing to look some of the stuff over adjust, add or delete some of that stuff, so that we could add it to tilesets.